LPCSTR, LPCTSTR and LPTSTR

Question

What the difference between LPCSTR, LPCTSTR and LPTSTR?

Why do we need to do this to convert a string into a LV / _ITEM structure variable pszText:

LV_DISPINFO dispinfo;  
dispinfo.item.pszText = LPTSTR((LPCTSTR)string);

Answer 1

Quick and dirty:

LP == Long Pointer. Just think pointer or char*

C = Const, in this case, I think they mean the character string is a const, not the pointer being const.

STR is string

the T is for a wide character or char (TCHAR) depending on compile options.

Answer 2

8-bit AnsiStrings

• char: 8-bit character - underlying C/C++ data type
• CHAR: alias of char - Windows data type
• LPSTR: null-terminated string of CHAR (Long Pointer)
• LPCSTR: constant null-terminated string of CHAR (Long Pointer)

16-bit UnicodeStrings

• wchar_t: 16-bit character - underlying C/C++ data type
• WCHAR: alias of wchar_t - Windows data type
• LPWSTR: null-terminated string of WCHAR (Long Pointer)
• LPCWSTR: constant null-terminated string of WCHAR (Long Pointer)

depending on UNICODE define

• TCHAR: alias of WCHAR if UNICODE is defined; otherwise CHAR
• LPTSTR: null-terminated string of TCHAR (Long Pointer)
• LPCTSTR: constant null-terminated string of TCHAR (Long Pointer)

So

| Item              | 8-bit        | 16-bit      | Varies          |
|-------------------|--------------|-------------|-----------------|
| character         | CHAR         | WCHAR       | TCHAR           |
| string            | LPSTR        | LPWSTR      | LPTSTR          |
| string (const)    | LPCSTR       | LPCWSTR     | LPCTSTR         |

Bonus Reading

TCHAR → Text Char

Answer 3

To answer the second part of your question, you need to do things like

LV_DISPINFO dispinfo;  
dispinfo.item.pszText = LPTSTR((LPCTSTR)string);

because MS's LVITEM struct has an LPTSTR, i.e. a mutable T-string pointer, not an LPCTSTR. What you are doing is

1) convert string (a CString at a guess) into an LPCTSTR (which in practise means getting the address of its character buffer as a read-only pointer)

2) convert that read-only pointer into a writeable pointer by casting away its const-ness.

It depends what dispinfo is used for whether or not there is a chance that your ListView call will end up trying to write through that pszText. If it does, this is a potentially very bad thing: after all you were given a read-only pointer and then decided to treat it as writeable: maybe there is a reason it was read-only!

If it is a CString you are working with you have the option to use string.GetBuffer() -- that deliberately gives you a writeable LPTSTR. You then have to remember to call ReleaseBuffer() if the string does get changed. Or you can allocate a local temporary buffer and copy the string into there.

99% of the time this will be unnecessary and treating the LPCTSTR as an LPTSTR will work... but one day, when you least expect it...

Answer 4

To answer the first part of your question:

LPCSTR is a const string

LPCTSTR is a const TCHAR string, (TCHAR being either a wide char or char depending on whether UNICODE is defined in your project)

LPTSTR is a (non-const) TCHAR string

This is a great codeproject article describing C++ strings (see 2/3 the way down for a chart comparing the different types)

Answer 5

Adding to John and Tim's answer.

Unless you are coding for Win98, there are only two of the 6+ string types you should be using in your application

• LPWSTR
• LPCWSTR

The rest are meant to support ANSI platforms or dual compilations. Those are not as relevant today as they used to be.